In recent years, a significant industry has developed which involves the application of customer-selected designs, messages, illustrations, and the like (referred to collectively hereinafter as “images”) on articles of clothing, such as T-shirts, sweat shirts, and the like. These images may be commercially available products tailored for a specific end-use and printed on a release or transfer paper, or the customer may generate the images on a heat transfer paper. The images are transferred to the article of clothing by means of heat and pressure, after which the release or transfer paper is removed.
Heat transfer papers having an enhanced receptivity for images made by wax-based crayons, thermal printer ribbons, ink-jet printers, laser-jet printers, and impact ribbon or dot-matrix printers, are well known in the art. Typically, a heat transfer material includes a cellulosic base sheet and an image-receptive coating on a surface of the base sheet. The image-receptive coating usually contains one or more film-forming polymeric binders, as well as, other additives to improve the transferability and printability of the coating. Other heat transfer materials include a cellulosic base sheet and an image-receptive coating, wherein the image-receptive coating is formed by melt extrusion or by laminating a film to the base sheet. The surface of the coating or film may then be roughened by, for example, passing the coated base sheet through an embossing roll.
Much effort has been directed at generally improving the transferability of an image-bearing laminate (coating) to a substrate. For example, an improved cold-peelable heat transfer material has been described in U.S. Pat. No. 5,798,179, which allows removal of the base sheet immediately after transfer of the image-bearing laminate (“hot peelable heat transfer material”) or some time thereafter when the laminate has cooled (“cold peelable heat transfer material”). Moreover, additional effort has been directed to improving the crack resistance and washability of the transferred laminate. The transferred laminate must be able to withstand multiple wash cycles and normal “wear and tear” without cracking or fading.
Various techniques have been used in an attempt to improve the overall quality of the transferred laminate and the article of clothing containing the same. For example, plasticizers and coating additives have been added to coatings of heat transfer materials to improve the crack resistance and washability of image-bearing laminates on articles of clothing.
Heat transfer materials have also been developed that include a transfer film that is peelable from the heat transfer material after imaging of the film but prior to the process of transferring the image to the substrate. Removal of the imaged peelable transfer film prior to adhering the film to the substrate attempts to solve the problem of image reversal that occurs when an imaged heat transfer material is placed image side down against the substrate for transfer of the image to the substrate. It also attempts to solve the problem of how to apply images to dark substrates because it allows an opaque layer to be placed behind the imaged surface of the peelable transfer film. The peelable transfer film allows the imaged film to be placed image side up against the substrate. A protective sheet may be utilized over the imaged film during the application of the heat and pressure used to permanently affix the film to the substrate. However, because the image is on the outside layer of the film, the ink or other medium is susceptible to exposure after the transfer. Exposure of the image medium can result in poor washability and wear characteristics. This may be partially solved by utilizing ink-receptive layers that allow inks to penetrate the film. However, penetration of the inks into the film may result in a decrease in brightness of the transfer, making it appear “chalky”, “washed out”, or less vivid.
Therefore, there remains a need in the art for heat transfer papers and methods of application that provide good image appearance and durability.